Revert link removal

denisvasilik · denisvasilik · commit 3a035891f021 · 2020-09-02T18:51:53.000+02:00
diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
@@ -449,6 +449,7 @@ pub trait Iterator {
     /// }
     /// ```
     ///
+    /// [`once`]: crate::iter::once
     /// [`OsStr`]: ../../std/ffi/struct.OsStr.html
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
